Cardiac surgery-associated acute kidney injury (CSA-AKI) is the most common clinically important complication in adult patients undergoing open heart surgery, and is associated with increased mortality and morbidity. In patients in intensive care units, CSA-AKI is the second most common type of AKI after septic AKI. In this Review, we explore the definition of CSA-AKI, discuss its epidemiology and identify its risk factors. We discuss current theories of the pathophysiology of CSA-AKI and describe its clinical course. Furthermore, we introduce diagnostic tools with particular reference to novel biomarkers of AKI and their potential utility; we analyse currently applied interventions aimed at attenuating AKI in patients undergoing cardiac surgery; and describe evidence from randomized controlled trials aimed at preventing or treating CSA-AKI. Finally, we explore issues in the use of renal replacement therapy, its timing, its intensity and its preferred modalities in patients with CSA-AKI, and we discuss the prognosis of CSA-AKI in terms of patient survival and kidney recovery.